Pulverized fuel burners for the partial oxidation of pulverized fuels are known which are ignited by an externally-arranged pilot burner.
Patent DD 285 523 describes a generic pilot burner for partial oxidation of gaseous hydrocarbons to gases containing CO and H2 in a pressurized bioreactor.
This pilot burner consists of coaxial channels for combustion gas and oxidation means which are open towards the reaction chamber and are separated or encased by channels through which water flows. Arranged in the combustion gas channel is an ignition cable which is connected to a high-voltage ignition system outside the burner and which, at its end facing towards the reaction chamber, turns into a metallic electrode which is routed up to the burner tip and forms a spark path here to the metallic wall. The electrode of this burner is positioned in the combustion gas channel so that it passes through the confuser, annular nozzle and diffuser forming the nozzle and has its spark path to the metallic wall at the radius of curvature of the diffuser in parallel to the axis, i.e. in the eddy area which forms the transition to the oxygen channel. The arrangement of the metallic electrode is chosen so as to enable the direct ignition of the combustion gas/oxygen on the one hand and on the other hand for the metallic electrode to be cooled by the combustion gas flowing onto it.
The high-voltage ignition cable is introduced into the burner through two separate pressure seals. The pressured area thus produced is used as a safety zone to prevent the escape of combustion gas leaks and is monitored on the pressurized side.
Further combinations of a combination burner consisting of an ignition, pilot and pulverized fuel burner are described in:    Sino German Gasification and CDM Forum held on 5-6 Aug. 2004 in Beijing “Lignite and Coal Gasification for Syngas and Energetic Gas Production” and    Chinese Patent Application No. CN 200510079702.4 dated 24 Jun. 2005 from the Beijing Aeronautical Power Inst. “Powder-combustable vortex burner”
The flame signal is transmitted to the monitoring device by means of a multistrand optical fiber cable.
The weaknesses of the known pilot burner are as follows:
The flame signal is transmitted from the reaction chamber to the flame monitor by means of an optical fiber cable, which, because of its proximity to the flame, is subject to thermal stress and can simultaneously also be restricted by soot particles occurring in the field of vision. In addition the metallic electrode located in front of the viewing window obstructs a free view into the reaction chamber.
For reasons of space the metallic electrode must be embodied as a wire which has numerous bends up to its electrode tip. This unstable shape means that the exact adjustments to the sparkover point necessary for ignition can only be made with difficulty. This gives rise to ignition faults and the functional integrity of the burner is not always guaranteed.
The design of the water-cooled nozzle (confuser, cylinder and diffuser) is very complicated and leads especially in the diffuser to thermal stresses which lead to cracks forming in the material and thus to the failure of the burner.
The arrangement of the electrode tip within the diffuser of the nozzle means that an eddy area necessarily forms at this point which mixes proportions of oxygen with the fuel and thus forms an ignitable mixture that can be ignited. It there are media fluctuations during ignition the eddy area moves and thus the mixing point moves as well, which results in ignition faults. This means that there is inherently a high susceptibility to faults.
The combination burner according to the Chinese patent application No. CN 200510079702.4 is further characterized by the pilot burner gas as well as the associated oxygen flowing to the mouth of the burner through a common channel in the center of the burner. The great danger of this is that, if the flow velocity changes, as occurs during start-up and shutdown, a re-ignition occurs in the burner channel, which leads to its destruction, with considerable danger to operating safety.